The present invention relates to injectors for injecting fuel in the fluid state, in particular the liquid state, for the purpose injecting the fuel directly into a combustion chamber of a controlled ignition engine. It is particularly applicable to injecting gasoline, but it can also be adapted to other liquid fuels, such as alcohol-based fuels and liquefied petroleum gas.
Direct injection injectors are already known comprising an injector body containing a needle that is axially displaceable by electrical control means (often constituted by a coil) and terminated by a shutter member, often of hemispherical shape, that co-operates with a fuel flow seat. The needle is displaceable between a first axial position in which the shutter element bears against the seat and a position in which it is spaced apart therefrom.
The stresses imposed on the injector for direct injection are much higher than those for indirect injection into a manifold. It is necessary both to limit the penetration depth of the fuel jet, e.g. to avoid wetting the walls of the chamber, and to ensure mixing that is as intimate as possible between the air and the fuel for better combustion, and to do this even though the time available for fuel injection is very short.
To achieve this result, attempts have already been made to impart turbulent motion to the fuel. Document WO-A-96/36808 describes an injector performing that function. It has a swirling chamber for putting the fuel into rotation about the axis of the shutter element, which chamber is situated upstream from the seat so as to avoid the presence of a dead volume between the seat and the spray hole.